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Loans and Allowance for Credit Losses - Troubled Debt Restructuring is 90 Days or More Past Due (Detail) (USD $) In Thousands, unless otherwise specified | 3 Months Ended
--- | ---
Mar. 31, 2013 Contract | Mar. 31, 2012 Contract
Financing Receivable, Recorded Investment, Past Due [Line Items] |  |
Number of Contracts | 2 | 2
Recorded Investment | $ 16 | $ 980
Real estate construction [Member] |  |
Financing Receivable, Recorded Investment, Past Due [Line Items] |  |
Number of Contracts | 0 | 2
Recorded Investment | 0 | 980
Loans to individuals [Member] |  |
Financing Receivable, Recorded Investment, Past Due [Line Items] |  |
Number of Contracts | 1 | 0
Recorded Investment | $ 6 | $ 0

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- Definition Troubled debt restructuring number of contracts 90 days past due. + References No definition available. + Details
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- Definition Troubled debt restructuring recorded investment ninety days past due. + References No definition available. + Details
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Namespace Prefix: | fcf_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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- Details
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Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration